This invention relates to the field of signal processors for radar receiving systems and communication systems, and more particularly relates to a sidelobe cancellation circuit used to suppress the effects of multiple interference sources being received by the main channel antenna.
Commonly, adaptive control loops are used to generate cancellation signals in response to interference signals. Typical null steering apparatus is described in U.S. Pat. No. 3,209,990 by P. W. Howell for "Intermediate Frequency Sidelobe Canceller". Apparatus of this type is used both in radar systems and in communication systems. See "Adaptive Arrays--An Introduction", by W. F. Gabriel in Proceedings of the IEEE, Vol. 64, No. 2, February 1976, pp 239 et seq. for a good introductory description, including the LMS algorithm.
S. M. Daniel, U.S. Pat. No. 4,070,675, shows a narrow beam main antenna that uses a wide beam array to enhance the performance of the main antenna in a jamming environment. D. D. Howard, U.S. Pat. No. 3,435,453, discloses an electronically scanned array which achieves sidelobe cancelling by using a wide beam auxiliary pattern with a narrow main beam pattern.
Other U.S. Pat. Nos. relating to sidelobe cancellers with a main antenna and multiple auxiliary antennas include 4,097,866; 4,170,755 and 4,177,464 by myself and others. These patents are incorporated by reference.
A problem that can limit sidelobe cancellation performance in real environments is the geometrical location of interfering sources with respect to the auxiliary array. It can be shown that a wide spaced auxiliary array is effective in cancelling closely spaced jammers but results in a substantial loss in performance at jammer locations corresponding to the array grating lobes. A closely spaced array reduces the grating lobe problem but shows a loss in sensitivity in cancelling closely spaced jammers. These two dual problems have been called geometrical anomalies.
In a realistic multiple jammer environment, both widely and closely spaced jammers may exist with random relative power distributions in the vicinity of the auxiliary array.